The localization problem is to determine an assignment of
coordinates to nodes in a wireless ad-hoc or sensor network that is
consistent with measured pairwise node distances.
Most previously proposed solutions to this problem assume that the nodes
can obtain pairwise distances to other nearby nodes using some ranging
technology. However, for a variety of reasons that include
obstructions and lack of reliable omnidirectional ranging, this
distance information is hard to obtain in practice. Even when pairwise
distances between nearby nodes are known, there may not be enough
information to solve the problem uniquely.

This paper describes MAL, a mobile-assisted localization
method which employs a mobile user to assist in
measuring distances between node pairs until these distance
constraints form a “globally rigid” structure that guarantees a
unique localization. We derive the required constraints on the
mobile's movement and the minimum number of measurements it must
collect; these constraints depend on the number of nodes visible to
the mobile in a given region. We show how to guide the mobile's
movement to gather a sufficient number of distance samples for node
localization. We use simulations and measurements from an indoor
deployment using the Cricket location system to investigate the
performance of MAL, finding in real-world experiments that MAL's
median pairwise distance error is less than 1.5% of the true node
distance.